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17-year-old (female) with sudden loss of consciousness

by Mohammad Hajighasemi-Ossareh, MD, MBA

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    00:02 A 17 year old girl suddenly holds her chest and collapses to the ground while playing volleyball at school.

    00:09 A nurse who was present at the scene rushes to evaluate the situation and realizes that the girl has no pulse and isn't breathing.

    00:18 The nurse starts chest compressions immediately.

    00:21 An automated external defibrillator(AED) is brought to the scene within three minutes and a shock is delivered.

    00:28 The girl regains consciousness and a regular sinus rhythm.

    00:32 She is rushed to the emergency department.

    00:34 In the emergency department, her heart rate is 65 beats per minute, it's regular and her blood pressure is 122/77 mmHg.

    00:44 EKG shows a shortened PR interval, a wide QRS complex, a delta wave and an inverted T wave.

    00:52 Which of the following is the most likely pathology in the conduction system of this patient's heart? Answer choice (A) - automatic discharge of irregular impulses in the atria (B) - impulse generation by tissue in the AV node (C) - Wandering atrial pacemaker (D) - Accessory pathway from atria to ventricles or (E) blockage in the conduction pathway Now take a second to come to your own conclusion Now let's discuss the question characteristics here.

    01:26 Now looking at the subject, this patient seems to have a cardiovascular concern and they're telling us about ecg findings, thus this is likely a cardiovascular question.

    01:36 Now this question is a 2-step question which means that we have to make one conclusion, and then go one step deeper to then find the correct solution and the stem is required in this case.

    01:48 We can't just read the last sentence and know the answer, we have to rely on the details in the clinical vignette.

    01:55 Now let's do our walkthrough.

    01:57 the first thing we need to do is determine the underlying characteristics at patient's presentation Now the patient is young and otherwise healthy as far as we know.

    02:06 The main event that's described in the clinical vignette is sudden loss of consciousness with immediate recovery and she even has a normal pulse and normal blood pressure right after recovery but that's after delivery of defibrillator shock.

    02:20 Now an abnormal ECG persist beyond recovery and it includes a shortened PR interval, a wide QRS complex and delta waves which are abnormal upstrokes of the QRS Now this suggests accelerated electrical impulses from atria to ventricles.

    02:42 Now, patient's presentation in this case can be summarized as what's called an acute reversible arrythmic event.

    02:51 Now this is in the context of what appears to be an underlying electrical conduction abnormality Now the second step we need to do is, we need to figure out what type of electrical conduction abnormality does this patient have? Well, the EKG shows that the conduction abnormality involves impulses between atria and ventricles While the electrical conduction upstream to the atria appears to be normal There is no P wave abnormalities but there is a short PR interval, and that's when you have atrial depolarization to the time of beginning ventricular depolarization.

    03:29 Also, we have a wide QRS,which is when you have complete depolarization of the ventricles so that that means that there is some type of abnormality between the conduction times in which the atria and the ventricles are involved.

    03:44 Now, given the combination of reversibility of arrythmia immediately after shock and EKG findings discussed already, this shows that the pathology here is excessive electrical firing, making an accessory pathway from the atria to the ventricle, the most likely etiology here for this patient.

    04:06 Now having an accessory pathway from atria to ventricles is the pathophysiology in a condition known as Wolff-Parkinson-White syndrome which is the most likely conduction abnormality for this patient.

    04:19 And thus the answer choice is (D) - accessory pathway from the atria to the ventricles.

    04:26 Now let's discuss some high-yield facts for this question.

    04:30 Wolff-Parkinson-White Syndrome is a condition in which there is electrical conduction abnormally in the heart in which it uses an accessory pathway between the atria and the ventricles that actually bypasses the AV node Normally, electricity goes from the atria to the ventricles through the AV node, but in WPW or Wolff-Parkinson-White, we have an accessory pathway that goes around the AV node and goes quicker from the atria to the ventricle hence the shortened PR interval in this patient's description.

    05:07 Now, bypassing the AV node, where in the AV node, usually the impulse waits before being propagated further, conduction to the accessory pathway travels at a significantly higher rate than what we would normally expect.

    05:22 When this conduction creates an electrical circuit or loop, the result is supraventricular tachycardia and accessory symptoms.

    05:31 Now delta waves on EKG are pathognomonic for WPW or Wolff-Parkinson-White.

    05:37 Now athough most people with accessory pathway never show symptoms.

    05:42 WPW is one of the most common causes of tachycardia in young patients.


    About the Lecture

    The lecture 17-year-old (female) with sudden loss of consciousness by Mohammad Hajighasemi-Ossareh, MD, MBA is from the course Qbank Walkthrough USMLE Step 1 Tutorials.


    Author of lecture 17-year-old (female) with sudden loss of consciousness

     Mohammad Hajighasemi-Ossareh, MD, MBA

    Mohammad Hajighasemi-Ossareh, MD, MBA


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